The invention relates to a device according to the preamble of claim 1. A device of this kind is in known from U.S. Pat. No. 5,005,577.
Measurements of intraocular pressure (glaucoma) are normally conducted on a routine basis during a visit to an eye specialist. In patients with known glaucoma, pressure measurements are performed at regular intervals of 6 to 12 weeks. These pressure measurements however are not very informative since the intraocular pressure varies with time of day. To obtain objective information as to whether a pathological pressure situation exists, continuous pressure measurements must be performed over a long period of time and a decision can be made on their basis as to whether therapy should be initiated, and what kind. This is not possible with the devices currently available for measuring intraocular pressure (tonometers).
The available tonometers (applanation and impression tonometers) permit an exact determination of the intraocular pressure (Grehn, F., Leydhecker, W. xe2x80x9cAugenheilkundexe2x80x9d [Ophthalmology], 26th edition, Springer Verlag, pp. 244-5). Their practical reliability for routine early detection is limited, however. With the known measuring devices, the cornea of the eye which is sensitive to pain is touched during measurement so that pressure measurement can be performed only following local anesthesia of the eye. The known measuring devices provide values that can not be used, when the surface of the cornea is abnormal as a result of edema or scars or in astigmatism. Investigations following operations on the eye to monitor the success of the operation are not possible. Non-contact clinometers currently on the market do not achieve the measurement accuracy required for a reliable diagnosis. Especially in the high pressure range which results in irreversible damage to the optic nerves, measurements with the currently available non-contact tonometers are too inaccurate and unreliable. Since the applanation of the cornea is used for measurement in these clinometers as well, they suffer from the disadvantages associated with this applanation.
The device described at the outset known from U.S. Pat. No. 5,005,577 includes a remote measurement device that can be implanted in an eye using an intraocular lens, said device containing a pressure sensor, a device that converts the sensor signals into information that can be transmitted without wires, and a transmitter. By means of a receiver located outside the eye, the information transmitted by the transmitter that can be implanted is received and converted into data on the intraocular pressure that can be recorded. In addition, the known device can have an energy source supplied from outside, for example a photoelectric element, to produce an active sensor and telemetric transmitter for data transmission.
In order to perform objective evaluation as to whether a pathologic optical situation exists in the eye, pressure measurements must be evaluated that cover a long period of time. Acquisition of these long-term pressure measurements is cumbersome with the known devices.
Hence the goal of the invention is to provide a device for measuring intraocular pressure with which an elevated intraocular pressure (glaucoma) can be monitored continuously and called up as necessary.
This goal is achieved according to the invention by the characterizing feature of claim 1.
Using the data logger in the implanted remote measurement device, continuous recording and storage of the measured values are performed over a long period of time. These data can be called up as necessary within a short space of time, for example within seconds to minutes. It is only during this period of time that an auxiliary device, in the form of a manual device, spectacles, or an eye bandage must be used to receive the measured data.
The remote measuring device which is preferably designed for active telemetry can be located at a suitable point, for example the sulcus of the capsule or the anterior chamber, as an implant that can be installed by surgery. This implant can be in the form of an intraocular lens, with the remote measuring device being provided outside the optical part of the lens, preferably at a haptic margin surrounding the lens part. This creates an intelligent lens for multifunctional measured value acquisition by active telemetry and integration of the data logger by which measured values can be stored.
Suitable sensors are those that allow determination of the intraocular pressure. In particular, the pressure sensor or pressure sensors, in contrast to the known capacitive measuring sensors (Sensors and Actuators A, 37-38 (1993) 93-105) can be created using surface micromechanics. In addition, electrodes for stimulation and derivation of stimulus potentials can be provided. The pressure sensor, the corresponding signal processing circuit, the data logger, and the telemetry components in the sensor, especially the coil and capacitors, are preferably integrated monolithically in a chip, for example a silicon chip. By inductive signal and energy transmission between the implanted remote measuring device and the receiving device provided outside the eye, active telemetry is obtained with the power supplied to the remote measuring device in the eye by inductive energy transmission. For this purpose, both the implanted remote measuring device and the receiving device located outside the eye have suitably designed antennas in the form of coils (ring coils).
Continuous measurement of intraocular pressure over several stages is possible without continuous data callup to the outside being necessary. With the data logger integrated into the active telemetry, data can be stored and called up at specific times, once a week for example. The implanted sensors can be calibrated without an external device, using self calibration. No spectacles need be worn for calibration. The energy supplied is reduced in active telemetry. Interference with the measurement is reduced by the monolithically integrated design. The measuring device is EMV tolerant. With a preferred surface micromechanical solution, the likelihood of the sensors breaking is reduced. In addition, surface-micromechanical sensors can be made in that sizes required for implantation. With the monolithically integrated design, silicon chips can be made thin enough to fit in the eye implant, especially an intraocular lens. The power can be supplied by inductive energy transmission from outside so that no battery is required.